Visual masking at different polar angles in the two-dimensional Fourier plane.
Human contrast thresholds were measured at 86 points in the two-dimensional Fourier plane with and without masks. The test stimuli were sinusoidal gratings in a 2.55-deg circular field. The superimposed masks were sinusoidal gratings having a polar spatial frequency of 8 cycles/deg, a contrast of 0.31, and one of five polar angles: 90, 105, 120, 135, and 180 deg. The test grating contrast for 75.5% correct detection in a three-alternative, forced-choice paradigm was determined by a maximum-likelihood adaptive psychophysical procedure. Three other observers were tested on subsets of these conditions. The threshold elevation surfaces produced by the masks lead to the following conclusions: spatial-frequency bandwidth is independent of mask orientation and has a value of approximately 2 octaves, orientation bandwidth is wider for oblique masks than for horizontal and vertical masks, the principle of spectral polar separability is violated, and two-dimensional Gabor functions in the frequency domain account for the masking effects. Individual differences were found among the observers.
Harvey
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Department of Psychology, University of Colorado, Boulder 80309-0345.
Doan
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D000328:Adult; D015350:Contrast Sensitivity; D005583:Fourier Analysis; D006801:Humans; D008297:Male; D010470:Perceptual Masking; D012684:Sensory Thresholds; D014785:Vision, Ocular